Weld3D

Weld3D is a classic Fusion 3D processor: required SceneInput accepts scene3d and Output remains scene3d. MediaIn or Background does not connect here directly; ordinary RGBA data appears only after Renderer3D.

The documented use case is duplicated or nearly coincident position vertices that should have been shared. These faults can appear as a hard shading edge, a crack under Displace3D, missing or doubled render pixels, or tiny gaps that affect downstream geometry interactions.

In Weld mode the tool joins vertices by position. Blackmagic explicitly notes that Weld3D does not weld normals, texture coordinates, or other vertex streams, so matching positions do not automatically repair shading or UV seams.

That boundary matters for diagnosis: if a hard edge remains after the positional seam is repaired, inspect normals/smoothing or the authored mesh rather than blindly increasing tolerance.

Weld Mode = Fracture performs the inverse operation: shared vertices become independent and polygon adjacency is lost. A connected ImagePlane3D made of quads, for example, becomes a set of unconnected quads. This is a topology operation, not an automatic shatter animation.

Auto Tolerance is the safest baseline. The historical Blackmagic Tool Reference recommends automatic detection for most cases. Disabling auto enables a manual Tolerance workflow; the exact conditional Resolve 21/21.1 UI remains a target-build live-verification item.

Tolerance is not an artistic strength control. If it is too large, unrelated nearby vertices can be welded and edges or faces can collapse. Increase it only as far as needed for a demonstrated near-duplicate seam.

Blackmagic describes Weld3D as a mesh robustness tool rather than a mesh-editing or simplification tool. If the gap is already clearly visible in the 3D Viewer, using a huge tolerance to pull the points together is usually the wrong repair strategy.

Weld3D is not Reduce Mesh. Positional welding is not controlled decimation/remeshing and should not be used as a general polygon-count optimization technique.

Order relative to Transform3D can matter in practice. The historical tool reference warns that vertices very far from the origin can become harder to match because of floating-point precision, so it is sensible to repair the mesh in local coordinates before applying a large downstream world-space placement.

Duplicated positions are not always errors. Sharp seams or special shading boundaries may intentionally store multiple vertices at the same position with different normals or attributes. Aggressive welding can therefore make lighting worse instead of better.

Fracture also needs intent. Removing adjacency can be useful for a topology workflow, but downstream deformation or smoothing may change because formerly shared corners are now independent vertices.

The bundled Resolve Inspector capture confirms Weld Mode with Weld/Fracture choices plus Auto Tolerance. Manual Tolerance is not visible in that capture, so its exact current conditional UI is not presented as already live-certified.

For diagnosis, A/B topology and shading evidence is stronger than a single beauty still: bypass the node, inspect wireframe or mesh structure, use simple lighting, and test the downstream operation where the defect originally appeared.

If a crack disappears but shading remains wrong, separate the causes: position continuity may already be fixed while normals, tangents, and UVs remain independent vertex streams.

Renderer3D is still the data boundary. Weld3D.Output can continue through Transform3D, Merge3D, ReplaceNormals3D, UVMap3D, and other compatible 3D processors; MediaOut and normal 2D effects belong after Renderer3D.Image.

This authoring pass did not execute a live Resolve 21/21.1 validation. Exact conditional Tolerance UI and behavior on specific production meshes remain target-build verification items rather than claimed live-certified facts.